The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Astronomical Changes in the Seasons

We notice changes in the seasons when we feel changing temperatures, discern difference in the length of the daylight period and see the transformation of the environment as plants blossom, grow and senesce. However, to better appreciate the astronomical changes that occur throughout the year, it helps to observe the changing positions of sunrise or sunset.

This set of sunset panoramas was taken in 2008 from Algonquin Island in Ontario, Canada, looking north. Algonquin Island is part of the Toronto island chain that sits 1.3 miles (2 km) south of the downtown Toronto shoreline.

The top panorama was taken on the date of the northern summer solstice, June 20, 2008. The Sun set at 304 degrees in azimuth -- not quite reaching the northwest direction or 315 degrees. It's adjacent to the landmark CN Tower. Of course, the summer solstice is the day of the year having the longest daylight period.

The middle panorama was snapped on the date of the autumnal equinox, September 22, 2008 (Northern Hemisphere). Sunset occurred due west at 270 degrees in azimuth, at a position further removed from the Toronto skyline. At the equinoxes, the length of day and night is very nearly the same.

The bottom panorama was taken on Christmas Day in 2008, four days after the date of the northern winter solstice. The Sun set at 238 degrees azimuth -- not quite reaching the southwest direction or 225 degrees. Note that it's well away from the downtown skyline. The Sun reaches its southernmost position in the sky on the date of the winter solstice, and as a result, in the Northern Hemisphere this is the day having the shortest daylight period.